Showing papers by "Marc A. Meyers published in 2008"

Mechanical Behavior of Materials

Abstract: A balanced mechanics-materials approach and coverage of the latest developments in biomaterials and electronic materials, the new edition of this popular text is the most thorough and modern book available for upper-level undergraduate courses on the mechanical behavior of materials To ensure that the student gains a thorough understanding the authors present the fundamental mechanisms that operate at micro- and nano-meter level across a wide-range of materials, in a way that is mathematically simple and requires no extensive knowledge of materials This integrated approach provides a conceptual presentation that shows how the microstructure of a material controls its mechanical behavior, and this is reinforced through extensive use of micrographs and illustrations New worked examples and exercises help the student test their understanding Further resources for this title, including lecture slides of select illustrations and solutions for exercises, are available online at wwwcambridgeorg/97800521866758

Biomedical applications of titanium and its alloys

Abstract: Titanium alloys are considered to be the most attractive metallic materials for biomedical applications. Ti-6Al-4V has long been favored for biomedical applications. However, for permanent implant applications the alloy has a possible toxic effect resulting from released vanadium and aluminum. For this reason, vanadium-and aluminum-free alloys have been introduced for implant applications.

Structure and Mechanical Properties of Selected Biological Materials

Abstract: Mineralized biological tissues offer insight into how nature has evolved these components to optimize multifunctional purposes. These mineral constituents are weak by themselves, but interact with the organic matrix to produce materials with unexpected mechanical properties. The hierarchical structure of these materials is at the crux of this enhancement. Microstructural features such as organized, layered organic/inorganic structures and the presence of porous and fibrous elements are common in many biological components. The organic and inorganic portions interact at the molecular and micro-levels synergistically to enhance the mechanical function. In this paper, we report on recent progress on studies of the abalone and Araguaia river clam shells, arthropod exoskeletons, antlers, tusks, teeth and bird beaks.

Mechanical strength of abalone nacre: Role of the soft organic layer

Abstract: The nacreous portion of the abalone shell is composed of calcium carbonate crystals interleaved with layers of viscoelastic proteins. The resulting structure yields unique mechanical properties. In this study, we focus on the thin viscoelastic layers between the tiles and on their role on the mechanical properties of the shell. Both SEM and AFM show that the thin (approximately 30 nm) organic layer is porous, containing holes with diameter of approximately 50 nm. These holes enable the formation of mineral bridges between adjacent tile layers. The mineral bridges play a pivotal role in growth and ensure the maintenance of the same crystallographic relationship through tile growth in the 'terraced cone' mode. The existence of mineral bridges is consistent with the difference between tensile and compressive strength of the abalone. Mechanical tests with loading applied perpendicular to the plane of the organic layers reveal a tensile strength lower than 10 MPa, whereas the compressive strength is approximately 300-500 MPa. These nanoscale bridges have, by virtue of their dimensions (50 nm diameter x 30 nm length), a strength that reaches their theoretical value. The calculated tensile strength based on the theoretical strength predicts a bridge density of approximately 2.25/microm(2). A major conclusion of this investigation is that the role of the organic layer is primarily to subdivide the CaCO(3) matrix into platelets with thickness of 0.5 microm. Its intrinsic effect in providing a glue between adjacent tiles may not be significant.

Shear Localization in Dynamic Deformation: Microstructural Evolution

Abstract: Investigations made by the authors and collaborators into the microstructural aspects of adiabatic shear localization are critically reviewed. The materials analyzed are low-carbon steels, 304 stainless steel, monocrystalline Fe-Ni-Cr, Ti and its alloys, Al-Li alloys, Zircaloy, copper, and Al/SiCp composites. The principal findings are the following: (a) there is a strain-rate-dependent critical strain for the development of shear bands; (b) deformed bands and white-etching bands correspond to different stages of deformation; (c) different slip activities occur in different stages of band development; (d) grain refinement and amorphization occur in shear bands; (e) loss of stress-carrying capability is more closely associated with microdefects rather than with localization of strain; (f) both crystalline rotation and slip play important roles; and (g) band development and band structures are material dependent. Additionally, avenues for new research directions are suggested.

High-strain, high-strain-rate flow and failure in PTFE/Al/W granular composites

Abstract: Dynamic compression experiments were performed on a pressed PTFE/Al/W mixture to understand the composite behavior at high-strain and high-strain rate. The high-strain-rate tests were carried out in a drop-weight apparatus at impact velocities of 3.5 and 5 m/s, providing strain rate so f approximately 4 × 10 2 s −1 . Aluminum jackets of varying thickness were used to ensure that specimens underwent confined deformation but did not separate into fragments. Failure was preceded by extensive plastic deformation concentrated primarily in the PTFE component. W particle–PTFE interface separation provided initiation and propagation of cracks. In extensively deformed specimens (strains of up to −0.875), PTFE nanofibers formed along cracks as a result of shear localization and significant softening caused by plastic deformation. The Zerilli–Armstrong constitutive equation for polymeric solids was used to simulate the response of the composite. Its use is justified by the fact that the majority of plastic strain is concentrated in the PTFE polymer. © 2007 Elsevier B.V. All rights reserved.

Transmission Electron Microscopy Study of Strain-Induced Low- and High-Angle Boundary Development in Equal-Channel Angular-Pressed Commercially Pure Aluminum

Abstract: The evolution of the microstructure in a commercially pure aluminum during equal channel angular pressing (ECAP) using route BC was investigated by transmission electron microscopy. Subgrains, or cells, form, which have both high (ϕ > 15 deg) and low (ϕ < 15 deg) misorientation. Misorientations and spacings of cell boundaries were determined from about 250 boundaries per pass of ECAP cell boundaries on the basis of Kikuchi patterns and Moire fringes. The average cell size and misorientation saturate within the first two passes. Misorientations and spacings of high-angle boundaries decrease with the number of passes. After eight passes, the cell size is ≈1.3 μm and the fraction of high-angle boundaries is ≈0.7. The marked differences in the rate of grain structure evolution per pass are linked to differences in the ability of dislocations introduced in new passes to recombine with the existing ones. With increasing ECAP strain, the distribution of misorientations develops strong deviations from the MacKenzie distribution for statistical grain orientation. This is interpreted as a result of the tendency to form equiaxed grains in a textured grain structure.

The cutting edge: Sharp biological materials

Abstract: Through hundreds of millions of years of evolution, organisms have developed a myriad of ingenious solutions to ensure and optimize survival and success. Biological materials that comprise organisms are synthesized at ambient temperature and pressure and mostly in aqueous environments. This process, mediated by proteins, limits the range of materials at the disposal of nature and therefore the design plays a pivotal role. This article focuses on sharp edges and serrations as important survival and predating mechanisms in a number of plants, insects, fishes, and mammals. Some plants have sharp edges covered with serrations. The proboscis of mosquitoes and stinger of bees are examples in insects. Serrations are a prominent feature in many fish teeth, and rodents have teeth that are sharpened continuously, ensuring their sharpness and efficacy. Some current bioinspired applications will also be reviewed.

The development of residual stresses in Ti6Al4V-Al3Ti metal-intermetallic laminate (MIL) composites

Abstract: Residual stresses in the metal (Ti6Al4V)-intermetallic (Al3Ti) laminate composite are generated when cooled from the processing temperature (∼700 ◦ C) to ambient temperature, because of the difference in thermal expansion coefficients between Ti6Al4V and Al3Ti. Two stress release mechanisms, creep and crack propagation, are proposed to explain the development of residual stress during cooling process. Both analytical calculations and finite element simulations are performed. In the analytical modeling, a critical stress criterion is proposed in order to determine the initiation of crack propagation. In the finite element simulation, the J-integral is used as a criterion for crack evolution; it enables the establishment of the distribution of the residual stress as a function of temperature. The results of both analytical modeling and finite element simulation show good agreement with the experimental results obtained through X-ray diffraction. © 2007 Published by Elsevier B.V.

Deformation Substructures and Their Transitions in Laser Shock–Compressed Copper-Aluminum Alloys

Abstract: It is shown that the short pulse durations (01 to 10 ns) in laser shock compression ensure a rapid decay of the pulse and quenching of the shocked sample in times that are orders of magnitude lower than in conventional explosively driven plate impact experiments Thus, laser compression, by virtue of a much more rapid cooling, enables the retention of a deformation structure closer to the one existing during shock The smaller pulse length also decreases the propensity for localization Copper and copper aluminum (2 and 6 wt pct Al) with orientations [001] and $$ [\ifmmode\expandafter\bar\else\expandafter\=\fi{1}34] $$ were subjected to high intensity laser pulses with energy levels of 70 to 300 J delivered in an initial pulse duration of approximately 3 ns The [001] and $$ [\ifmmode\expandafter\bar\else\expandafter\=\fi{1}34] $$ orientations were chosen, because they respectively maximize and minimize the number of slip systems with highest resolved shear stresses Systematic differences of the defect substructure were observed as a function of pressure, stacking-fault energy, and crystalline orientation The changes in the mechanical properties for each condition were compared using micro- and nanohardness measurements and correlated well with observations of the defect substructure Three regimes of plastic deformation were identified and their transitions modeled: dislocation cells, stacking faults, and twins An existing constitutive description of the slip to twinning transition, based on the critical shear stress, was expanded to incorporate the effect of stacking-fault energy A new physically based criterion accounting for stacking-fault energy was developed that describes the transition from perfect loop to partial loop homogeneous nucleation, and consequently from cells to stacking faults These calculations predict transitions that are in qualitative agreement with the effect of SFE

Structural biological materials: Overview of current research

Abstract: Through specific biological examples this article illustrates the complex designs that have evolved in nature to address strength, toughness, and weight optimization. Current research is reviewed, and the structure of some shells, bones, antlers, crab exoskeletons, and avian feathers and beaks is described using the principles of materials science and engineering by correlating the structure with mechanical properties. In addition, the mechanisms of deformation and failure are discussed.

Effect of strain rate on the compressive mechanical properties of aluminum alloy matrix composite filled with discontinuous carbon fibers

Abstract: Compression and forced shear loading were utilized to investigate the quasi-static and dynamic response of carbon fiber/Al–Mg composites. Two types of carbon fibers (PAN-based (CPAN ) and pitch-based (CPitch)) were introduced into an Al–Mg alloy matrix (∼30 vol% fibers). The CPAN /Al–Mg composite had higher compressive and shear strengths than CPitch/Al–Mg regardless of fiber orientation. The difference in strength due to the nature and probably quality of the fibers was more significant than the effect of fiber orientation (perpendicular or parallel to loading direction). The compressive strength of these composites exhibited a strain rate sensitivity comparable with that of an Al–Mg alloy and more pronounced for the CPAN /Al–Mg composite. The microstructural features of shear flow in the localized shear zone in hat-shaped specimens and the characteristics of fractured fibers are analyzed and discussed. Possible reaction of the metal matrix and carbon fibers was observed. © 2007 Elsevier B.V. All rights reserved.

Combustion synthesis/quasi-isostatic pressing of TiC–NiTi cermets: processing and mechanical response

Abstract: TiC-NiTi composites were produced by a technique combining self-propagating high-temperature synthesis (SHS) of elemental powders of Ni, Ti, and C with densification by quasi-isostatic pressing (QIP). In order to create a one-step synthesis/densification process, the Ti ? Ni ? C reactant material was surrounded in a bed of graphite and alumina particulate before initiation of the combustion reaction. The sample was ignited within the particulate and subjected to a uniaxial load immediately after passage of the combustion wave. The constitutive response, composition and resulting structures of the composites with varying volume fractions of NiTi are characterized. Powder mixtures prepared anticipating the formation of stoichiometric TiC result in the formation of composites with a eutectic matrix of Ni3Ti and NiTi. This titanium impoverishment of the matrix is consistent with the formation of nonstoichiometric TiCx during the com- bustion reaction. The Ni3Ti phase can be suppressed by anticipating the formation of TiC0.7 and adjusting the chemical content of the reactant mixture to include addi- tional titanium. These cermets combine the high hardness of the ceramic phase with the possible shape memory and superelastic effects of NiTi. Introduction and objectives

MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF PTFE/Al/W SYSTEM

Abstract: Mechanical and microstructural properties of high density PTFE/Al/W composites consisting of PTFE matrix, aluminum and tungsten particles were investigated. Three types of samples having different porosities and particle sizes of W with an identical weight ratio between PTFE, Al and W were fabricated by Cold Isostatic Pressing. The quasi‐static and Hopkinson Bar compression tests were employed to investigate the mechanical properties of these materials. The results demonstrated that the porous PTFE/Al/W composite samples containing fine W particles have higher quasi‐static and dynamic fracture stresses than higher density PTFE/Al/W samples containing coarse W particles. ESEM micrographs revealed that deformation occurred mainly in the PTFE matrix while metal particles remain undeformed. We observed nano‐fibers of PTFE caused by high strain rate deformation.

Combustion synthesis/quasi-isostatic pressing of TiC0.7–NiTi cermets: microstructure and transformation characteristics

Abstract: TiC0.7–NiTi cermets were produced by combustion synthesis followed by quasi-isostatic consolidation while the reaction products were still hot and ductile. The TiC0.7–NiTi cermets were characterized by differential scanning calorimetry, room temperature transmission electron microscopy (TEM), and in-situ TEM (temperature varied during observation). The matrix of the as-synthesized 20NiTi, 40NiTi, and 60NiTi composites contains both R and B19′ martensites at room temperature. No distinct R-phase morphology could be imaged. In the B19′ martensite, [011] Type II twinning, \( (11\bar 1) \) Type I twinning and (001) compound twinning modes were observed as the lattice invariant shear (LIS) of the R-B19′ transformation. The [011] Type II twinning is often reported as the LIS of the B2-B19′ transformation, but this is the first experimental confirmation of its predicted presence as a qualified LIS of the R-B19′ transformation. The (001) compound twinning mode is responsible for the fine structure of the martensite with a wavy morphology. Nanoscale structures with a thickness of 5 nm were obtained inside the twins. Twinning was also observed at the interface with carbide particles, which confirms that some stress relaxation of the elastic mismatch occurs. At room temperature, the matrix of the 80NiTi composite had the R-phase structure, which appeared with a needle-like morphology. Thermal cycling resulted in the suppression of the R-phase transformation. This is the opposite of the behavior observed in un-reinforced NiTi alloys.

Experiments for the validation of debris and shrapnel calculations

Abstract: The debris and shrapnel generated by laser targets are important factors in the operation of a large laser facility such as NIF, LMJ, and Orion. Past experience has shown that it is possible for such target debris to render diagnostics inoperable and also to penetrate or damage optical protection (debris) shields. We are developing the tools to allow evaluation of target configurations in order to better mitigate the generation and impact of debris, including development of dedicated modeling codes. In order to validate these predictive simulations, we briefly describe a series of experiments aimed at determining the amount of debris and/or shrapnel produced in controlled situations. We use glass and aerogel to capture generated debris/shrapnel. The experimental targets include hohlraums (halfraums) and thin foils in a variety of geometries. Post-shot analysis includes scanning electron microscopy and x-ray tomography. We show the results of some of these experiments and discuss modeling efforts.

Mechanical Behavior of Materials: Creep and Superplasticity

Abstract: Introduction The technological developments wrought since the early twentieth century have required materials that resist higher and higher temperatures. Applications of these developments lie mainly in the following areas: Gas turbines (stationary and on aircraft), whose blades operate at temperatures of 800–950 K. The burner and afterburner sections operate at even higher temperatures, viz. 1,300–1,400 K. Nuclear reactors, where pressure vessels and piping operate at 650–750 K. Reactor skirts operate at 850–950 K. Chemical and petrochemical industries. All of these temperatures are in the range (0.4–0.65) T m , where T m is the melting point of the material in kelvin. The degradation undergone by materials in these extreme conditions can be classified into two groups: Mechanical degradation . In spite of initially resisting the applied loads, the material undergoes anelastic deformation; its dimensions change with time. Chemical degradation . This is due to the reaction of the material with the chemical environment and to the diffusion of external elements into the materials. Chlorination (which affects the properties of superalloys used in jet turbines) and internal oxidation are examples of chemical degradation. This chapter deals exclusively with mechanical degradation. The time-dependent deformation of a material is known as creep . A great number of high-temperature failures can be attributed either to creep or to a combination of creep and fatigue. Creep is characterized by a slow flow of the material, which behaves as if it were viscous.

Mechanical Behavior of Materials: Elasticity and Viscoelasticity

Abstract: Introduction Elasticity deals with elastic stresses and strains, their relationship, and the external forces that cause them. An elastic strain is defined as a strain that disappears instantaneously once the forces that cause it are removed. The theory of elasticity for Hookean solids – in which stress is proportional to strain – is rather complex in its more rigorous treatment. However, it is essential to the understanding of micro- and macromechanical problems. Examples of the former are stress fields around dislocations, incompatibilities of stresses at the interface between grains, and dislocation interactions in work hardening; examples of the latter are the stresses developed in drawing, and rolling wire, and the analysis of specimen–machine interactions in testing for tensile strength. This chapter is structured in such a way as to satisfy the needs of both the undergraduate and the graduate student. A simplified treatment of elasticity is presented, in a manner so as to treat problems in an undergraduate course. Stresses and strains are calculated for a few simplified cases; the tridimensional treatment is kept at a minimum. A graphical method for the solution of two-dimensional stress problems (the Mohr circle) is described. On the other hand, the graduate student needs more powerful tools to handle problems that are somewhat more involved. In most cases, the stress and strain systems in tridimensional bodies can be better treated as tensors, with the indicial notation.

Void Growth in Single and Bicrystalline Metals: Atomistic Calculations

Abstract: MD simulations in monocrystalline and bicrystalline copper were carried out with LAMMPS to reveal void growth mechanisms. The specimens were subjected to both tensile uniaxial and hydrostatic strains; the results confirm that the emission of (shear) loops is the primary mechanism of void growth. However, these shear loops develop along two slip planes (and not one, as previously thought), in a heretofore unidentified mechanism of cooperative growth. The emission of dislocations from voids is the first stage, and their reaction and interaction is the second stage. These loops, forming initially on different {111} planes, join at the intersection, the Burgers vector of the dislocations being parallel to the intersection of two {111} planes: a 〈110〉 direction. Thus, the two dislocations cancel at the intersection and a biplanar shear loop is formed. The expansion of the loops and their cross slip leads to the severely work hardened layer surrounding a growing void. Calculations were carried out on voids with different sizes, and a size dependence of the stress response to emitted dislocations was observed, in disagreement with the Gurson model[1] which is scale independent. Calculations were also carried out for a void at the interface between two grains.

Chemical reactions in controlled high-strain-rate shear bands

Abstract: Controlled high-strain-rate shear bands were generated in porous mixtures (Nb+Si, Ti+Si) using axially symmetric experimental configurations (“Thick-Walled Cylinder”) method. Shear strains up to 100 and strain rates of approximately 107 sec−1 were generated inside shear bands. Particle fracture, melting, and regions of partial reaction were observed inside shear bands for the Nb+Si system. Under the same conditions of deformation, for the Ti-Si system the reaction initiated inside shear bands and propagated through the entire sample.